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Date:   Mon, 8 Feb 2021 20:44:16 -0700
From:   Nathan Chancellor <nathan@kernel.org>
To:     Alexei Starovoitov <ast@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>,
        Andrii Nakryiko <andrii@kernel.org>
Cc:     Martin KaFai Lau <kafai@fb.com>, Song Liu <songliubraving@fb.com>,
        Yonghong Song <yhs@fb.com>,
        John Fastabend <john.fastabend@gmail.com>,
        KP Singh <kpsingh@kernel.org>,
        Nick Desaulniers <ndesaulniers@google.com>,
        netdev@vger.kernel.org, bpf@vger.kernel.org,
        clang-built-linux@googlegroups.com,
        Veronika Kabatova <vkabatov@redhat.com>,
        Jiri Olsa <jolsa@kernel.org>
Subject: FAILED unresolved symbol vfs_truncate on arm64 with LLVM
Message-ID: <20210209034416.GA1669105@ubuntu-m3-large-x86>
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Hi all,

Recently, an issue with CONFIG_DEBUG_INFO_BTF was reported for arm64:
https://groups.google.com/g/clang-built-linux/c/de_mNh23FOc/m/E7cu5BwbBAAJ

$ make -skj"$(nproc)" ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- \
                      LLVM=1 O=build/aarch64 defconfig

$ scripts/config \
    --file build/aarch64/.config \
    -e BPF_SYSCALL \
    -e DEBUG_INFO_BTF \
    -e FTRACE \
    -e FUNCTION_TRACER

$ make -skj"$(nproc)" ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- \
                      LLVM=1 O=build/aarch64 olddefconfig all
...
FAILED unresolved symbol vfs_truncate
...

My bisect landed on commit 6e22ab9da793 ("bpf: Add d_path helper")
although that seems obvious given that is what introduced
BTF_ID(func, vfs_truncate).

I am using the latest pahole v1.20 and LLVM is at
https://github.com/llvm/llvm-project/commit/14da287e18846ea86e45b421dc47f78ecc5aa7cb
although I can reproduce back to LLVM 10.0.1, which is the earliest
version that the kernel supports. I am very unfamiliar with BPF so I
have no idea what is going wrong here. Is this a known issue?

Cheers,
Nathan